Spin trapping is a powerful and convenient technique for the study of free radical reactions. The breadth of applications ranges from clinical studies to high-energy physics. Over 1500 references to the technique have accumulated in Chemical Abstracts. STDBII, a spin trapping database, has been implemented on IBM PC/AT and MacIntosh personal computers. The package operates with no 'add-ons.' The program is powerful yet user-friendly; the command structure is similar to the familiar 1-2-3 light-bar menu; search strategy employs the method of Query-by-Example (QBE) ; logical combination of any fields is accomplished by using AND, OR, NOR, and EXCEPT. Presently, STDBII (4.0) contains files for 5,5-dimethylpyrroline-N-oxide (DMPO), alpha-phenyl-N-tert-butyl nitrone (PBN), 2-methyl-2-nitrosopropane (MNP), alpha-(4pyridyl-1-oxide)-N-tert-butyl nitrone (POBN), nitrosodurene (ND) and 3,5-dibromo-nitrosobenzene sulfonate (DBNBS). Data for other less popular traps are included in a catch-all file. Our goal is to incorporate all published work that relates to spin trapping. Presently, the database files have more than 1500 references with over 5500 parameter entries. The STDBII files contain information on: 1) spin trap used; 2) radical trapped; 3) hyperfine splittings reported; 4) solvent; 5) g-value, if reported; 6) a terse summary on how the radical was produced and observed; 7) full bibliographic data; and 8) retraction on anything by the author. STDBII helps researchers: 1) in identification of spin adducts from the sometimes unique hyperfine splitting parameters; 2) as a key to the spin trapping literature 3) as a vehicle to correct published errors. STDBII is now available to researchers both inside and outside NIEHS. The package includes a user manual that lists all of the compiled information on spin trapping. Scientists who do not presently have access to an IBM/PC can still benefit from STDBII because all of the database entries are printed in the STDBII User Manual.